Conventionally, a nitride or an oxide dielectric layer are well known materials which are used to form protective or anti-reflective thin film layers, both of which are manufactured using the sputtering plating method.
As shown in FIG. 1, a conventional optical magnetic disk includes a substrate (or a transparent printed circuit board) 5. A first anti-reflective layer 6, formed from a nitride dielectric material, such as, SiN.sub.x is coated on substrate 5 in a thickness of about 800-1000.ANG. on which a recording layer 7 is placed and covered by about 300.ANG. of an amorphous RE-TM alloy, such as Tb, Fe and cobalt.
Also, a second anti-reflective layer 6a formed from a nitride dielectric layer of SiN.sub.x is placed upon the recording layer 7. A reflective layer 8, composed of metals, such as Aluminum (Al), Chromium (Cr) and Titanium (Ti) etc., is formed on the second anti-reflective layer 6a. The structure of FIG. 1 has a Kerr rotation angle (.theta.k) and a Faraday effect (.theta.f) due to the characteristics of the amorphous RE-TM material which is used with the recording layer 7.
When a laser beam passes through the substrate 5 of FIG. 1, the beam reaches the surface of the recording layer 7 by passing through the first anti-reflective layer 6, on which the beam is partly reflected and enhances the Kerr rotation angle (.theta.k). The beam is also partly transmitted to improve the Faraday effect (.theta.f). The reflective index, the permeability and the thickness of the first and the second anti-reflective layers 6 and 6a of FIG. 1 are detrimental to the Kerr rotation angle (.theta.k) and the Faraday effect (.theta.f).
SiN.sub.x or SiO materials have been used as the first anti-reflective layer 6 and the second anti-reflective layer 6a and create a problem because the reflective index (n) which adapts to the Kerr rotation (.theta.k) and the Faraday effect (.theta.f) is lowered by about 1.5-2.0.
If the reflective index (n) of materials used in the first and second anti-reflective layers 6 and 6a is increased, the Kerr rotation angle (.theta.K) and the Faraday effect (.theta.f) will also be increased. However, the inherently inferior reflective index of SiN.sub.x or SiO deteriorates the magnetic optical characteristics of the disk structure.